Hey Blinky, I got one for ya. I'm not sure how to correct it because I don't really know how to recreate it. Here is the situation:

A kid who lives on my block has one of those weedeater engine powered scooters. He flies up and down the block sporadically. My GSD will be mid nap, here him coming and bolt to the front yard fence and chase him the length of my yard barking (I have a fenced in front yard). I just got a text from my girlfriend who stopped by my house to do me a favor and while going in the house, the kid goes by on the scooter. My dog is gone. 2 blocks later he stops chasing and turns and she picks him up. Scolded him and he has been pouting ever since, she says. However, what concerns me is that last week, I came home, opened the gate to pull my truck in, and a kid on a bike goes by and he chases him down too. Absolutely no aggression, his tail is wagging and he thinks its a fun game. Prior to these 2 instances, he sit and stays while we pull a car into the yard. People have walked by, cars have driven by, kids have been playing in the street (which he struggles with his "stay" cause he wants to play with them so badly, but he never actually gets up). Any advice? He scared the snot out of both kids (when I say kids, they are 16ish) cause this 80 lb GSD is running at them and they don't understand that he just thinks they are playing.

Thanks Blinky.

I'm curious, does this only happen with those particular scooters or does it happen with people on bikes or non-powered scooters? I'm wondering if it is the sound coupled with the motion or just the sight of a single person traveling at that speed triggering the behavior.